


Welcome to the Sin Bin

by Worlds_Okayest_Writer



Category: Undertale (Video Game)
Genre: F/F, F/M, Fontcest, M/M, Requests, There's also fluff though so give or take, Underfell, underswap - Freeform, undertale - Freeform, you feel your sins crawling on your back
Language: English
Status: In-Progress
Published: 2016-10-01
Updated: 2016-10-04
Packaged: 2018-08-18 22:12:44
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings, Rape/Non-Con
Chapters: 3
Words: 4,410
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/8177986
Author URL: https://archiveofourown.org/users/Worlds_Okayest_Writer/pseuds/Worlds_Okayest_Writer
Summary: Shorts, drabbles and requests for Undertale.





	1. Gettin' the Train Rollin' (Leave your requests here)

Hey folks, thanks for having a look-see at this heap of sin and garbage of mine! I'd like to start by saying requests are currently open, and I'm taking suggestions.  
I'll probably only get to the ones I really like cause I'm selfish and lazy, but don't be afraid to throw me a suggestion!

I will accept any kinda ship, fontcest is okay, as are crack ships. Any and all! There are only a few ships I genuinely dislike. And I'll label each chapter accordingly, so if some of the subject matter bothers you, ya can just skip it easy peasy.

The type of content found here will change, depending on my mood. Fluffy cuteness to explore character dynamics, plotless smut, a short story to explore an idea further, etc. All kinda of stuff, scenarios and fetishes will be explored here, nothing is sacred! And if there's anything in particular that you'd like to see, just ask! Worst I'll say is that I don't like the ship/whatever you're requesting lol.

Along with that, as I post more stories and cover more things, I'll add tags and stuff accordingly.

Anyway, thanks for stopping by and I hope to hear from the lot of ya!

EDIT: Actually, screw the legend lol. I'll just put the warnings on the summary up top and the important stuff in the title, like super triggering stuff (Rape, torture, incest etc.) so, yeah.


	2. "You're Late" Gaster/Sans, Non-Con

**Summary for the Chapter:**

> Here's the first one, for Sansisaprettygirl, hope you like this man :D
> 
> This was my first attempt at a fanfic, so... yeah. Woop.  
> Also, forgive the ugly ass formatting here, I'm still trying to figure out this site's HTML and stuff. It's weird.
> 
> Warnings/whatever: Non-Con/Dub-Con, tentacles, sensitive bones

The lab was cold when Sans stepped inside, sending a shudder up his spine. He had been late again today, though just a few minutes. He hoped it was enough that his boss wouldn’t notice. As he swiftly crossed the lab floor, darting around tables pulled together and chairs randomly dotting, he found himself sweating. Letting out a shaking sigh he dropped his bag onto the floor beside his desk, flicking the skinny lamp on with a loud click.  


It felt as if a weight were hanging around his neck all morning, hands trembling and sweat dotting his brow. His boss, Dr. Gaster, had so far been a pretty decent guy. He never raised his voice, never seemed to get angry, but there was such an incredible weight to his presence. When he glided around the desks, nimbly avoiding every chair leg with ease, there wasn’t a soul in the room who didn’t notice him. Sans most definitely was unable to keep his focus on his work when the doctor was nearby. The burning violet of his eye lights scorching him as he tried to work, shaking so hard his bones rattled. To put it simply, Dr. Gaster was quite intimidating.  


With a loud sigh, Sans dropped down into his swivel chair, sockets narrowed down at the stack of papers laying halfhazardly across the surface of his desk. The very same he had left last night, frustrated from his lack of progress on this report. The Doc had asked him days ago to compile this research for him, and while it was an incredible honor to be asked such by Dr. Gaster, he couldn’t help but feel the pressure it put on him. Any mistake at all that he could make on that report would reflect upon his superiors and even potentially, Dr. Gaster himself.  


The hush that permeated the room that morning was thick, unnerving. No matter what he tried Sans couldn’t get so much as a smile from anyone around him. Something must have happened earlier this morning, something no one was ready to discuss. If it was bad enough that the whole crew of interns were curling in on themselves, Sans couldn’t imagine how badly it must be effecting the Doc. He got really into this science mess, taking his own projects very seriously.  


A hand falling onto his shoulder woke him from his thoughts with a start. It was the youngest intern, a golden skinned lizard monster, trembling in her over-sized lab coat.  


“Th-the-the doctor w-wants to ssss-see you, Sans.” She mumbled, quiet voice stumbling over itself.  


“oh uh, what? did he say what was up?” Sans asked, a shock of white hot dread shattering through his chest.  


“N-no he just- just said to send y-you in.”  


Oh, no. That wasn’t good. Sans thanked her quietly and rose from his chair, fighting hard to keep his bones from rattling together as his hands shook hard beneath his coat sleeve. The walk to the doctor’s personal office seemed like miles and miles of hallway, each one lit painfully brightly with fluorescent bulbs way above his head.  


Sans’s mind quickly began to wander as he walked, intentionally slowing his pace. Did the Doc know he was late today? Was late yesterday? Did he even care about tardiness? Despite the fact that he had been working underneath this man for months now, he really didn’t know much about him. What he did when he was truly angry, nor how to make him reach that point. No matter what kind of catastrophic meltdown happened in the labs, that cold and calculating expression never left his face. Nothing at all seemed to bother him.  


Maybe that’s why Sans found him so incredibly unnerving, but at the same time purely fascinating. He was far different than Sans himself, jokes never seemed to go far with the doc and his attitude was chilly at best. Though, he did often stop to speak to several of his underlings, so maybe he wasn’t all THAT bad? It was hard to say, honestly. His boss rarely spoke about anything aside from the projects currently being worked on.  


Sans found himself standing in front of his boss’s door, and hardly remembered how he got there. The sharp throbbing of his soul in his chest sped up, sending shocks across his bones. Damn, was he nervous.  


Trembling fingers found the strength to knock audibly on the door.  


“Come in.” Was the response, muffled by the wood.  


Trying – and failing – to curb his shaking, Sans pushed open the door. He didn’t know what to expect of the doc’s office but, this was close. The floor, ceiling and walls were all the same stark white color, the walls lined with metal shelves all filled to bursting with books and notepads. The doctor himself was leaning over his desk, peering fully focused into a microscope he had placed up top.  


“Take a seat, Sans. This will only take a moment. I did not expect you to arrive so quickly.”  


Sans could only nod, dropping awkwardly into one of the nearby chairs as he watched Dr. Gaster work. He was quite a bit taller and larger than Sans was, his spectral body filling out the entirety of his slim lab coat. Even now, leaning over to peer into his microscope, thin boney fingers pausing only to pick up a pen and scribble down onto a notepad, he looked positively regal. He couldn’t keep himself from staring, knowing it was rude. If the doc caught him, he’d have no excuse prepared.  


Seconds ticked by like minutes as the shorter skeleton watched the other work, scribbling notes onto his notepad. Finally he stood, placing the pencil down with a sigh. He shot a look at Sans, and he bristled. The expression was unreadable, almost empty. But there was something in the way his eyelights met Sans’s that made the smaller look away, unable to hold that impressive gaze.  


“It seems, upon my observation Sans… That you’ve been having difficulties adjusting to the new lab.” He finally spoke, placing a gloved hand flat against the top of his desk to lean against. Sans could only swallow, fingers curling around the sides of his chair in a tight grip.  


“i-i suppose i have.” Sans mumbled back, unable to meet the doctor’s gaze. Fingers curled gently under his chin, lifting his face up to meet those heavy violet eyes. Sans hadn’t even heard him move.  


“You’ll tell me if you need anything, Sans. Alright? I want my employees happy, and without stress.”  


“i- i’m sure i’ll be fine in the morning doc, j-just gotta get some rest or something. y’know?” The trembling in Sans’s voice bothered him more than he thought it would. Dr. Gaster let out a soft hum, a deep rumbling in his throat.  


“Yes, I do know. You need to loosen up.” Those words, spoken with a deep chuckle sent a shiver down Sans’s spine. He did not like how he said that.  


Before he knew what was happening, his back met the surface of the desk with a crunch, bones digging into the wood through his clothes. Thick, inky black tentacles wrapped around the smaller skeleton, his neck, arms, legs, all pinned down and away from his body. Stretched out like a frog in a biology classroom.  


“Ah- Doc what-“ Sans shouted, struggling against the incredibly strong hold of those tendrils of slimey ink. Dr. Gaster simply laughed, shoving Sans’s legs apart with a knee.  


“I’m going to give you the proper motivations to arrive on time for once.” The doctor’s voice a low rumble as he pressed his pelvis against the younger skeleton’s, the rise of Dr. Gaster’s iliac crest grinding up into Sans’s roughly. The pressure quickly drew a gasp from Sans, the intern twisting and writhing on the desk to escape the grasp of the doctor’s tentacles.  


Dr. Gaster stood still for a moment, gazing down at his intern. The heated flush of blue across his cheeks, the look of panic in his rapidly flashing eye lights, those sounds he was making… Such an interesting subject.  


Sans, however, wasn’t finding as much interest. The icy shards of panic splintered across his bones as his soul pounded, pace frantic.  


“P-please doc, don’t do this! I’ll be on time tomorrow, c’mon please!” Sans cried out, flinching as the doctor let loose a laugh that rumbled in his ribs.  


“Ohh no, Sans. I know you will.” Dr. Gaster leaned down over the struggling boy, boney fingers finding the hem of a shirt to slide underneath, rubbing gently over the ribs found there. Sans flinched. Dr. Gaster just chuckled.  


“Sensitive?” He asked, voice teasing. A certain laughter to it. He found all this so amusing. Sans stayed quiet, despite his rapid shallow breathing.  


This can’t be happening, not to him. Not right now.  


The doctor had his shirt pushed up to his cervical vertebra now, trailing finger tips teasing and taunting along the protrusions of Sans’s ribs, letting them jump from bone to bone causing the flushing boy to jump with every contact.  


Dr. Gaster smirked down at him, letting his hands gently brush and flick at the other’s bones, relishing in the whimpers he drew from him.  


“P-please…” Sans groaned, voice hitching in his throat as a tentacle reaches up into his ribcage and starts fucking squirming against his spine. With every coil, every shift of that slimey appendage, Sans cried out and flinched. It felt so good. Too good. His back was arching off the desk as more and more tentacles came and filled him, pushing almost painfully against the insides of his ribs. Spilling through them. Squirming and writhing as the doctor stood between his legs, watching with a twisted smile on his face.  


When those long fingers drooped down to pinch the tips of Sans’s iliac crest, the boy let out a strangled gasp. Finding this to be satisfactory, the doctor continued his assault on the boy’s protruding hip bones, kneading and massaging them as the younger skeleton squirmed beneath his touch.  


The tentacles inside Sans’s ribs suddenly vanished, leaving him gasping and shaking on the desk. The sensations that were previously sending pleasure shooting up and down his spine was missed with a twist of disgust, the lack of sensation leaving a dull buzzing in Sans’s bones. The doctor calmly stripped Sans of his pants, letting them slide down his legs and pool at the floor, before scooting back in – not quite as close as before. He could see the swelling of magic between the boy’s legs and laughed again. He had no idea he would be getting to Sans this badly, this quickly. How interesting.  


The remaining tentacles held fast to Sans’s limbs and neck as he fought to escape Dr. Gaster’s touch. His fingers found Sans’s iliac crest once again, letting them slide down and inside of his sacrum. The throbbing heat from the mound of magic at the base of his spine was tempting, but the doctor kept up his gentle, teasing ministrations of Sans’s bones. The flushing skeleton arched his back off the table as Dr. Gaster’s hands and fingers teased at his sacrum, playing at the tip of his coccyx, doing everything he could to elicit those sweet moans and whimpers from Sans.  


Finally, his fingers brushed, every so gently, against that pounding mound of magic at the base of Sans’s spine, drooling with lust and too much magic. Sans screamed. The rush of pleasure sparking up his spine rocketed his back off the desk, straining pitifully against the tentacles holding him down.  


“My my, what a reaction.” Dr. Gaster laughed, almost a giggle, as he flicked a finger through that coalescing magic to see that reaction again. The smaller skeleton’s body was glistening with sweat, tears he probably didn’t know he was shedding spilling down the sides of his darkened face. The colors of his eye lights flashing rapidly. Gods, that was good.  


The flood of thick, slick tentacles into Sans’s ribcage once again brought those delicious moans and Dr. Gaster bristled. What Sans wasn’t expecting was the sudden, rough barrage of tentacles into the cavity of his hips and sacrum. All of them pushing through that mound of magic inside him and twisting, coiling around his lower spine, slapping wetly against his iliac crests on both sides. The sounds from him were beastly, moaning and growling, gasping up at the ceiling as his hands pawed and clawed at the air, hunting for something to grip onto. To stable himself, balance against this barrage of pleasure and over stimulation.  


It was almost too much, this feeling. Pleasure coursed through his body, sparking hot fire up his spine. Mouth open in a soundless scream that was much too loud. He soon felt that build-up of pressure within him, deep down into the core of his magic, his soul. The mound of magic between his thighs clamped down hard on Dr. Gaster’s tentacles, and the taller skeleton gazed down at Sans in wonder and curiosity as he came, hard. His body writhed and screamed himself hoarse. That incredible pleasure, everywhere the tentacles touched him, inside his ribs, his pelvis, throat, all burned with pleasure fire.  


Dr. Gaster moaned deep in his throat as he watched his intern’s body rock with the pleasure he was forcing upon him, the look on the pinned boy’s face was incredible.  


Finally, after what felt like an eternity to Sans, the tentacles retreated, pulling from their places slowly, the final one sliding out of Sans’s pelvis with a wet, slick pop. The spent skeleton laid on the desk, limp as a wet noodle.  


“Now, clean yourself up Sans, you have a lot of work to get to.” The doctor chuckled, dropping a towel on the other’s face. Shame burning in his eye lights, Sans quickly wiped the slime off his bones and drew his clothes back up, rushing out of the office without a word, the only indicator to the events being the heat drawn across his face.

**Notes for the Chapter:**

> Alright well, now that that's outta the way...
> 
> This was fun to write :D I like tentacles~


	3. Good Boy (Fontcest, Underswap)

**Summary for the Chapter:**

> Hey sorry if this isn't what you were wanting, but I had a lot of fun with this. SO MUCH FLUFF.
> 
> Warnings, etc whatever: Foncest involving Underswap!Sans and Papyrus. Praise kink. Sensitive bones.

Papyrus woke to silence. Glancing about the room, he was momentarily confused by his surroundings, but the sleepy fog in his brain cleared in a few shakes of his head. He was in the living room, splayed out on the couch. Hoodie open, no shirt beneath to let the bones of his ribs and sternum kiss the cool air.

Standing, he stretched to his full length and flinched at the creaks and pops, nearly echoing in the empty air. It didn’t take long for him to realize Sans wasn’t home.

“Must be on patrol.” Papyrus mumbled to himself, gently rubbing an eye socket as he slipped into the kitchen. The fridge was stocked with tacos and other assorted food items, and strangely he felt turned off from the selection. Closing the fridge door with a sigh, he just reached up into the cabinet, boney fingers hunting for a bottle of sweet, delicious honey. Finding just what he was looking for, he slipped the cap off with a flick of his thumb and slid back into the living room, the couch calling his name like a forlorn lover. Dropping down onto the cushions, he grabbed up the remote and clicked on the TV.

He was unsure how much time passed as he sat flipping through channels, lazily sipping from his bottle of honey. The sound of the door unlocking made him sit up, glancing towards the door with half lidded eyes. Sans stepped inside, eye lights dim and head bowed. Closing the door behind him quietly, he shuffled into the house, stripping his bandana off his neck and letting it drop onto the back of the couch Papyrus was currently sitting on.

“You alright, blue?” He asked, throwing an arm over the back of the couch. He didn’t like seeing his brother like this, so down from his usual peppy energy.

“I’m fine.” He mumbled back, not at all convincing. His voice was soft. Papyrus immediately stood, placing a hand on the much shorter skeleton’s shoulder.

“What happened bro?”

“It was…” He sighed, shrugging his brother’s hand off his shoulder to vanish into the kitchen. Not wanting to pressure him, Papyrus slipped his hands into his hoodie pockets, heaving a sigh through his nasal cavities. He placed himself back on the couch, watching the door to the kitchen for him to come back out.

“It was just awful, brother!” Sans finally said, coming back out of the kitchen with a taco folded in his hands.

“She- I asked Alphys when she was going to consider letting me into the royal guard and…”

Oh boy, Papyrus thought, bringing a leg up to rest on the coffee table in front of him. Sans stood beside the couch, staring down at the taco in his hand.

“She told me… That I was t-too… nice to be a royal guard.” He finally said, placing the uneaten taco onto the coffee table and dropping heavily onto the couch cushions.

“I wouldn’t b-be able to fight anyone and- and I’d just get hurt.”

Papyrus stared over at his small little brother, frowning deeply. He was clearly upset, fighting off his tears. This wasn’t the time to make jokes, but he had to do something to cheer up his lil’ bro.

“Hey, blue. C’mere.” He said, reaching over to wrap his arms around the shaking skeleton. Gently, he pulled him over into his lap and held him close, feeling the younger boy start to cry, fighting hard not to make a sound.

“S’all right, man. I’ll talk to her tomorrow for ya, alright? We’ll get you into the guard bro.” Papyrus said, gently petting the back of Sans’s head as the younger leaned into him, pressing his face against the vertebra of his neck. He stayed there with him for a long time, letting Sans cry himself out. Occasionally rubbing up and down his spine to comfort him.

“Thanks Papyrus.” Sans finally said, letting his arms snake around his taller, older brother’s neck.

“No worries, bro.”

The sudden feeling of teeth raking against his vertebra make Papyrus stiffen. Sans’s teeth explored his neck bones, nibbling gently at the processes jutting from each individual bone.

“Ah-“ Papyrus groaned, letting his head tilt to the side. “Gettin’ a little frisky there huh, bro?” He said with a chuckle, letting his fingers slip under Sans’s shirt to find his lower spine. As his fingers deftly stroked and teased over his lumbar, Sans whimpered and arched his back, pressing his sternum into Papyrus’s bare chest. He chucked deep in his throat and teased up his brother’s spine, relishing in the squeaks and moans he tickled out of Sans.

“Besides bro, she’s a moron if she thinks you’re not good enough.” He said, trailing his fingers through Sans’s ribs beneath his shirt. The smaller skeleton sighed deeply, letting his head drop down onto Papyrus’s shoulder. Shifting around carefully, Sans found himself laying back against the cushions, staring up at his smiling brother. The look of adoration in his orange eyelights brought a heat to Sans’s cheeks.

“You’re just beautiful.” He finally said, taking Sans’s face into his palms to gently rub his temples with a thumb.

“Brother…” Sans whispered, averting his gaze.

“I mean it.” Pap’s sudden, forceful words brought Sans’s glittering blue eyelights back to his face. He was still smiling.

“There’s no one in the underground more incredible than you.” Papyrus leaned down, gently clicking his teeth against Sans’s forehead. Just as gently as the first, he dotted clicks and kisses across Sans’s burning face, cupping his jaw in his palms. Finally, his teeth found Sans’s and they pushed together, Sans drawing up to deepen their kiss. Summoning a tongue with ease, Pap let the orange appendage slip between Sans’s teeth, coiling around the other’s. Sans moaned softly as Papyrus’s tongue toyed with his, sliding across the slick surface. That skillful tongue slid over his molars, the roof of his mouth. Exploring him.

Bringing his hands up to grip at Papyrus’s loose open hoodie, Sans couldn’t help but arch up into him. They hadn’t spent time together like this in far too long.  


Pulling back for air, Papyrus sat up fully, straddling the younger skeleton, and he couldn’t help but smile. Taking all of his brother in. He really was just so incredibly.  


Laying there, pinned beneath his brother, Sans’s couldn’t help but feel overwhelmed by his brother’s stare.

Bringing a hand down to cup his cheek, Papyrus’s smile widened just a bit.

“You’re such a good boy, Sans.” He whispered, stroking a thumb across his cheek. Sans shuddered beneath Papyrus’s touch, nuzzling into his palm. He loved it when Papyrus got into this kind of mood. Feeling hands slip under his shirt, he glanced down to watch Papyrus’s deft hands moving up over his ribcage. The feeling of his fingers jumping softly over his bones sent a heat shivering across his body.

Pap leaned down over Sans again, sliding his teeth over Sans’s neck bones. His hands roamed the other’s body, pawing and teasing the ridges and notches and every inch of every bone, leaving Sans a panting blushing mess by the time those fingers found the hem of his pants. Sliding them down, Papyrus wasn’t at all surprised to find Sans’s magic was building up in his pelvis, a mound of magic practically drooling with need.

Dipping down, that orange conjured tongue glided over the panting smaller skeleton’s pelvis, avoiding that throbbing heat of magic for now. Sliding his pants entirely off, Papyrus had to pause to look at him. The way his body was trembling, bones gently rattling together. The heated flush across his face. Eyes filled with stars.

“You’re so beautiful, Sans.” Pap murmured, sliding his palms up the inside of those trembling femurs. He slowly got into position, tucking his arms under Sans’s femurs, still shaking from desire, and let his head fall between them. Tongue dancing over the front of his pelvis, he couldn’t help but smile from that whine that escaped his little brother.  
“I love those sounds you make, bro.” He laughed, gently nibbling at his hip bones. The sudden sensation of those teeth on his sensitive hips sent Sans’s back arching off the couch. He panted softly, covering his mouth with his hands. He wasn’t any quieter.

Pap’s tongue finally found that intensely burning mound of magic. As that nimble conjured tongue slid inside, Sans fought to keep his hips still. He desperately wanted to thrust up into that feeling, grind his bones against Papyrus’s face. But he kept still, the only indication of his desire was the hard shaking of his entire body. 

Tongue swirling, fingers gently teasing the tips of Sans’s iliac crest. Pap couldn’t help but moan into Sans’s pelvis. God, those sounds. The more intense he got with the ministrations of his tongue, the more incredible and loud Sans got. There was nothing Pap loved more than to hear those noises, knowing that he was bringing his brother such incredible pleasure.

Sans felt that sudden buildup in his pelvis, hot fire of pleasure coursing through his body. Back arching off the couch, hands twisting in Papyrus’s hoodie, Sans could barely contain this feeling. Mouth open in an almost constant moan, gasping for breath. He lost control of himself long ago, hips thrusting up into Papyrus’s face. The taller skeleton continued his moderate pace, tongue dancing inside, fingers playing with his sacrum, his hips, every inch he could reach.

“P-pap I… I’m gonna- I think I’m-“ Sans gasped out, his fists twisting in Pap’s hoodie. The only response he got was a low, growling moan from his older brother that vibrated through his entire pelvis. That was all it took. Sans came hard, a rush of pleasure shooting up his spine and scrambling his brain. Stars exploded in his vision, and he wasn’t even aware of the gasping moans coming from him.

Throughout the orgasm, Papyrus watched him, tongue still dancing inside him. The way his back arched, his hands gripping his hoodie, the flush across his bones, the moaning and gasping and whimpering… Papyrus lived for this moment.

After what felt like an eternity of agonizing pleasure, Sans came down from that orgasmic high. His back fell against the cushions and he shuddered, panting harshly up at the ceiling. Pap pulled back, letting his tongue slide from his brother’s pelvis as the magic slowly dissipated.

He felt the gentle tug of his bro’s fist in his hoodie and he got the message. Crawling up his form, he laid on top of Sans, curling his arms under his body as he clicked a kiss to his flushed, heated cheek.

“You’re so good, Sans.” He whispered, clicking kisses all over his face, neck and shoulders.

“I love ya, bro.”

Sans giggled, throwing his arms around his lanky brother’s neck.

“Give me a few minutes, Pap, and I’ll show you how much I love you back.”


End file.
